Method of and apparatus for forming gear teeth



Nov. 5, 1946. A. MACKM'ANN M0544 D A PPABATUS FOR FORMING GEAR TEETH METHOD OF AN 2 sheets-sheet 1 Filed April 4, 1942A Patented Nom-.5, 1946l Mn'rnon oF Ann arraan'rus Foa romvmrc enen 'rns'rn Arthur Mackmann,

Foote Bros. Gear ,an

Chicago, nl., assignor 'to d Machine Corporation,

Chicago, lill., a corporationofDelaware Application April 4, 1942, Serial No. 437,645

This invention relates to a method of and tool for forming gear teeth and more particularly to the iinishlng of gear teeth to provide a'smooth very accurate surface thereon. v

In the art of forming gear teeth it is the usual practice at the present time to cut the teeth in blanks by the use of toothed hobs or cutters. It is extremely difficult -to form the cutting teeth on such hobs accurately and is impossible Ato-keepthem accurate in use, particularly as any regrindmg or sharpening changes their size or configura- .,tion due to the necessity of relieving the teeth behind their cutting edges.

Therefore, to obtain accurate gear teeth, it has been necessary to use a shaving or finishing operation after hobbing the blanks.

Shaving or finishing tools for straight spur gear teeth have been employed which are moved back and forth along the length of the teeth vand withA which very satisfactory results can be obtained. Such tools, however, are expensive and have a short life, sharpening being 'very diiiicult and more than a very few resharpenings being impossible.

Finishing of Worm gears where a high degree of accuracy is required has heretofore been possible only by hand and this is a very tedious and expensive operation.

The present invention has to provide a method of and a to'ol for finishing gear teeth by which either worm or spur type gears can be finished quickly and erliciently with a high degree of accuracy.

Another object of the invention is to provide a tool for forming gear teeth which is relatively simple and inexpensive to manufacture and which will have a long useful life. According to one important feature the tool requires no relieving back of its cutting edges and can therefore be resharpened an indenite number of times until itis almost completely worn away.

Still another object of the invention is to pro- Y vide a method of and tool for forming gear teeth in which a cutting edge tangent to a base circle is moved about the center of the circle across the sides or faces of the teeth to be formed.

The above and other objects advantages and desirable features of the invention will be more readily apparent from the following description when read in connection with the accompanying drawings, in whch- Figure l is an end view of a tool embodying the invention;

Figure 2 is a side elevation of the tool;

Figure 3 is a top plan view illustratingthe cutting of a blank with the tool;

Figure 4 is a side elevation ,looking from the bottom of Figure 3;

Figure 5 is a view similar to Figure 3 illustrating the cutting of straight spur gear teeth;

io claims. (ol. zio-1.6)

for one of its objects Figure 6 is an elevation looking from the bottom of Figure 5;

in. re 'lis an end view of an alternative tl cons"` Action;

Figure 8 is a side view of and Figure 9 is a section illustrating engagement of the tool of Figures 'l and 8 with a gear.

According to the present invention,

the tool of Figure l in a blank are first formed as accurately as pos-- sible either by form cutting or hobbing or by any other one of the known conventional gear cutting processes to approximately their final shape and size and are then adapted to be finished to provide accurate tooth surfaces according .to the method of and with the tool of the present invention. The invention isillustrated in connection with involute or approximately involute gear teeth although it is Vapplicable also to other tooth Y forms.

The worm which is formed as-accurately as possible and which will tend to reproduce in the gear perfect mating surfaces. Since the worm tends to produce a constant velocity in the gear, its cutting or shaving action on the gear teeth willremove any irregularities in size, shape and eccentricity. Thus a gear may be finished on its working shaft and will be perfectly concentric therewith.

In order that the tool may cut or scrape the gear to remove material therefrom the flanks of the-teeth thereon are provided with one or more cutting edges lying along lines tangent to a cylinde'r coaxial with the tool. If such cutting edges were radial to the tool it would be necessary to relieve the tool body behind them in order to cut -but I have foundthat by cutting grooves or slots in the anks of the teeth along lines tangent tc a circle concentric with the tool no relief is necessary. In one preferred form the cutting edges are formed to lie in planes tangent to the base cylinder of the tool but this is not essential, it being suflicient that the cutting edges lie in planes tangent to any cylinder coaxial with the tool whether ofthe same size as or smaller'than the base cylinder of the tool. Another way ofexpressing the location of the cutting edges is that they lle in planes subtending chords less than a semi-cylinder in a cylinder circumscribing the outside diameter of the worm.

Figures l, 8 and 9 illustrate one form of tool embodying the invention, which comprises a cylindrical body lll having formed thereon helicoidal teeth il. As shown, in Figure 8, the tool is in the' form of a double worm but it will be understood that a worm form having one-or more helical teeth thereon can be utilized equally well.

The surfaces of the helical teeth on their opposite faces are formed with a series of gashes or tool employed constitutes in effect a master the gear teeth as to tooth 'gent at one side will exist in any cutting edge Y slots i 2 each lying substantially tangent to the cylindrical body I and extending throughout the Y y ber oi' timessimply by enlarging the-grooves or slots I2 on one or both sides thereof to renew the cutting edges. v

Figuresl and 2 which'is somewhat simpler and less expensive to manufacture than that of Figures 7 and 8 but which functions in substantially the same Way. This tool comprises a cylindrical body a double helical thread i5 thereon. Instead of or slots in the opposite thread faces, in this instance a plurality of elongated g'ashes or slots I 6 are cut throughout the length of the threads in a plane parallel to the axis of the cylindrical body and` lying substantially tanto the surface thereof. Ifde'- sired, in order to increase the number of cutting edges additional slots I1 similarly formed may be cut in the teeth between the slots I6. `yThe slots I6 and I1 are substantially identical except that the slots I6 extend throughout' the full tooth threads, the being to increase the strength teeth.

It will be noted particularly from Figure 2 that the cutting edges formedwby the slots I6 and I1 on one side of the teeth I5 lie in a substantially straight line as shown at I8, this line corresponding to the helicoidal line of action of the teeth. On the opposite side of the teeth, since the slots, are not truly tangent to the cylinno relieving of the teeth behind.

illustrate another type of tooll surface of the teeth to the outer ends thereof.

- 4 the tool formation. To three movements, namely, feeding rotation of the tool, of the tool radially into the gear, and

' relative movement along the tool, are all that are found that the resulta highly accurate and substantially no tool gear will have smoothV surface showing marks.

Il having l drical body at this point due to the helix angle of the teeth, the cutting edges formed by the slots are curved as shown at I9. This curvature not lying along the helicoidal` line of action of the worm tooth, as for example if the slots are cut tangent to acylinder other than the base cylinder of the tool, but Ihave found that the tool operates eniciently whether or not the cutting edges are straight or curved as shown. l

Figures 3 and 4 illustrate method of using this tool `to cut or shave teeth 22 on a blank 2|, which can be either a concave face worm gear or a helical spur gear. According to this method the cylindrical body I4 may be power driven by any suitable machine and the blank 2i may be mounted on a shaft 23 which is rotatable and which is arranged at right angles to the axis of the body I4. 'I'he tool mayy then be moved into :the body or conversely, the tool turning the body through the gear teeth 22 at a rate depending on the relative ratios therebetween. As soon as any tightness occurs shaving or cutting of the teeth 'to the axis of the body between the two relative extremes of movement indicated by dotted lines in Figure 3. rate of wear on the tool throughout its length and compensates for any minor inaccuracies in 'I'his operation produces an even 'I'he operation ask just 'described will form a `worm gear with a zero back lash relative to the result is to provide a load on the shaft 23 tending to resist turning thereof so that the tool Will tend to A shave a slightly excessive amount of metal from each side of the gear ing clearance when the gear is used with a Worm of the same size as the tool.

For cutting helical spur gear teeth an additional motion is introduced as illustrated in Figure 3 in a direction substantially parallel to the teeth on'the blank or gear shafts to the proper center distance.

When this additional the teeth on the gear blank will be formed unighout their length at an angle to shaft 23 determined by the helical pitch ofthe teeth I5 on the cutting tool and by the angle between the cylindrical body i4 and the shaft.

For cutting straight spur gear teeth, the gear blank, as shown at 24 in Figures 5 and 6, may be form a worm gear these` teeth thereby providmovement is introduced,

yof slightly larger section than" the comprises yforming on of precision worm gears by power driven machinery and the present invention provides such a process by which extremely "accurate gears can be produced rapidly and economically.

While two specific forms oi invention have been shown and described in detail, it will be understood that, numerous variations might be made therein and that the particular forms shown and described are illustrative only and are not to be taken as a definition of the scope ofthe invention, reference being had for this purpose to the appended claims. l'

What is claimed is: Y g l. The method of forming gear teeth which comprises forming ona blank a series of gear teeth substantially to the final tooth depth'butv nal tooth form, meshing with the teeth'on the blank the teeth of a master worm, forming in the flanks of the worm teeth cutting edges lying in planes substantially tangential to the base circle of the worm, and driving this worm in tight-mesh with the teeth of the gear blank so that as the worm is rotated said cutting edges will lie in the helicoidal line of action of the master worm to shave the gear teeth to a corresponding matingsurface.

2. The method of forming( gear teeth which comprises forming on a blank a series of. gear teeth substantially to the of slightly'larger section than the final tooth form, meshing with the teeth on the blank the teeth of a master worm, forming in the -flanks of the worm teeth cutting edges lying in planes substantially tangential to the base circle of the Worm, driving the worm and simultaneously causing relative movement between the blank and the master worm in a direction parallel to the axis of the worm.

3. The method of forming gear teeth which a blank a series of gear teeth substantially to the iinal tooth depth but of a section slightly form, forming on a base cylinder a helical tooth of a size and shape to mesh with teeth of the final tooth form, forming in the faces of said nal tOOth depth but Y section complementary to larger than the ilnal toothv helical tooth a plurality of cutting edges lying substantially tangent to the base. gaging the helical tooth with the teeth on the blank with the axes of the blank and the base cylinder spaced a greater distance than vthe normal center distance. rotating the' base cylinder, and moving the axes of the blank and the base cylinder together to -their normal vcenter distance.

teeth which on a blank'a series of gear to the ilnal tooth depth but than the final tooth 4. The method of forming gear comprises forming teeth substantially of a section slightly larger form, forming on a base cylinder a helical tooth of a size and shape to mesh with teeth o! the final tooth form, forming in the faces of said helical tooth a plurality of cutting edges lying substantially tangent to the base cylinder, engaging the helical tooth with the teeth on the blank with the axes of the blank and the base cylinder spaced a greater distance than the normal center distance, rotating the base cylinder, movingthe axes of the blank and the basecylinder together to their normal center distance, and simultaneously moving the blank and base cylinder relative to each-other in. adirection parallel to the axis of the base cylinder.

cylinder, en-

' the axes of the blank 5. The method of forming gear teeth `which comprises forming on a blank a series of gear teeth substantially to the iinal tooth depth but of a section slightly larger than the final tooth form, forming on a base cylinder a helical tooth of a size and shape to mesh with teeth of the nal tooth form, forming in the faces of said helical tooth a plurality of cutting edgeslying substantially tangent to the base cylinder, engaging the helical tooth with the teeth on the blank with and the base cylinder spaced a greater distance base cylinder and blank together to their normal center distance, and simultaneously moving', the blank and base cylinder relative to each other in a direction generally.- parallel to the length of the teeth on the blank.

v6. The method of forming gear teeth which comprises forming on a blank a series of gear teeth substantially to the final tooth depth but of a section slightly larger than the final tooth form, forming on a base cylinder a helical tooth of a. size and shape to mesh with teeth of the final tooth form, forming in the faces of said helical tooth a plurality of cutting edges lying substantially tangent-to the base cylinder, engaging the helical tooth with the teeth on the blank with the axes cylinder spaced a greaterdistance than the normal center distance, and simultaneously moving the blank and the base cylinder relative to each other in directions parallel to the axis oi the base cylinder and to the length of the teeth on the blank. l

' '1. A tool for forming gear teeth comprising a master worm having a helical tooth of a size and that of the teeth to be formed, the helical tooth having formed in its flanks cutting edges lying in planes tangent to the base cylinder of the worm and substantially coinciding with the helicoidal line of action4 of the tooth. v

Y 8. A tool for forming gear teeth comprising a master worm having a helical tooth of a size and `section complementary to that of the teeth to be formed, the helical tooth having cut away portions in its iianks to provide cutting edges in the flank surfaces in planes luder of the worm and substantially coinciding with the helicoidal line of action 9. A tool for forming gear teeth comprising a masterworm having a helical tooth of a size and to that of the teeth to tooth Yhaving a slot cut therein in a plane tangent tothe base cylinder oi' the worm and extending through the tooth to form cutting edges on both -anks thereof.

10. A tool for forming gear teeth comprising'a master worm having a helical tooth of a. size and section complementary to thatvof the teeth to be formed, the helical tooth having a plurality of slots extending through the several turns thereof and lying in planes tangent to the base cylinder of the worm, certain of the slots extending completely through the depth of the tooth into the worm body and the of the root of the worm thread.

ARTHUR. MACKMANN.

than the normal center distance. rotating the base cylinder, moving the of the blank and the base tangent to the base cy'l.-

of the tooth.

other slots terminating short 

